a) Field of the Invention
The invention is directed to transmission equipment with an optical transmission line to which a plurality of subscriber nodes are connected.
b) Background Prior Cut
Transmission equipment and diverse types of information transmission via transmission lines are known in general. Recently, optical transmission lines have become increasingly important for various reasons. In addition to the optical point-to-point connections, complicated network structures with optical lines are also known. For example, in an article entitled "Optical fibres in local area networks", Communications/Communications International, October 1985, pages 19 ff., B. Viklund describes various network structures with glass fiber cables for distribution networks and for networks with connections between diverse subscribers which can be set up individually. In the latter, a ring structure is most favorable. The subscriber stations of an optical transmission line of the aforementioned type are connected to the respective utilized fibers via optoelectrical couplers.
At present, there are components for optical systems, e.g. couplers, switches and modulators, based e.g. on GaAs semiconductor material which utilize electro-optical effects in order to influence light. These elements work up to frequencies in the gigahertz range (Gbit/s).
The use of address-coded packets for the transmission of information is generally known. Such packets comprise a header and an information part [hereinafter, infopart], wherein the header contains all necessary data for the respective packet and the participating devices, e.g. a destination or target address, data concerning the type of packet, monitoring bits, etc. The infopart is available for the useful information to be transmitted.
When receiving information arriving via an optical line it is unavoidable that at least a part of the light stream carrying the information is used. If the light stream on the transmission line is not regenerated in some way, then it is gradually reduced in reception nodes which are connected serially one after the other.
The connection and access nodes of such transmission equipment generally comprise electrical regenerators. The latter require optoelectrical and electro-optical transducers, so that, as a whole, this is rather a matter of mixed optical and electrical equipment.
The primary object of the invention consists in providing transmission equipment which makes do to a great extent without electrical regenerators while utilizing the aforementioned components. In this way, a system is to be provided which must be referred to as "optical" in a more literal sense than was previously the case.
This object is met by the characterizing part of the independent claims. The dependent claims show constructions of the invention.
The solution, according to the invention, makes it possible to provide flexible transmission equipment which has considerable advantages over the comparable, previously known equipment because of its more extensive optical construction. An outstanding immunity to electromagnetic interference and reduced jitter problems are to be mentioned in particular; there is also a reduction in interference sources caused by bit errors. In addition, the transmission equipment is extensively protected against the failure of individual subscriber nodes.
The invention is described in more detail in the following by way of example with reference to eight diagrams.